I'm doing Sebring again this year too! There is one official reststop on the 100 mile route, and lots of orange trees if you need more. The 12-mile loops take you right past restrooms on the race track. And, when we move onto the race track at night, there are another set of restrooms in the pit area (edit: where you pass by every 3 miles). That was the least of my problems at Sebring...